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Mamm Creek Pit 3 November 16, 2000 until a Department of the Army Permit is obtained, and it may be necessary to stipulate in the permit that wetlands disturbance may not occur until the permit is appropriately revised to include wetlands plans. As Tom Schreiner points out, it is important that the reclamation permit issued by the State not conflict in any way with a Department of the Atmy wetlands permit, since the State would be compelled to reclaim in accordance with the federal wetlands requirements in a bond forfeiture situation. If the wetlands reclamation plans of both agencies are in agreement, the Division of Minerals and Geology can assure that sufficient bond is in place to fulf-ill the requirements of the plans. One critical consideration of mining through wetlands and reclamation to replace disturbed wetlands is that wetlands soil requires special handling and must be stockpiled separately from all other soil or overburden. Soil salvaged from wetlands must be used only for wetland reconstruction. Careful handling must be employed to preserve the integrity and viability of the wetlands soil, to assure [hat all usable soil is salvaged and stockpiled in a safe location (see Rule 3.1.9(3)), and to assure that the wetlands soil is not mixed with sand, gravel or other types of soil. 6. The application proposes certain unmined barriers between the edge of the pit and various features that must be protected from mining related impacts. The 50 foot wide bamer from the edge of the pit [o the CDOT right-of-way is adequate as long as the depth of n:fining does not exceed 25 feet. The application indicates that the depth of mining will exceed 25 feet at the west end. The Division recommends that the Operator set back a horizontal distance from the right-of-way that is equal to 2-times the pit depth. The horizontal setback distance should be measured from the toe of the pit slope or highwall to avoid a potential violation of the setback if some minor slumping of the edge of the pit occurs. The Division generally imposes a requirement to setback two times the pit depth when critical structures are involved and in the absence of an engineering demonstration that a lesser setback is appropriate (see Rule 6.5). The proposed 100 foot setback from the mining operations [o the Colorado River will be adequate to protect the river banks and channel from adverse impacts during normal flows, but it is not clear from any information provided in the application whether the pits would capture the river during a flood event. Capture of the river by the mined out pits could result in destabilization of banks and channels through [he mining reach and also for considerable distances up and downstream. Gravel mining within 400 feet of a major stream must consider the potential for channel capture. Reference is made to Urban Drainage and Flood Control District, "Technical Review Guidelines for Gravel Mining Activities within or Adjacent to 100-Year F7oodplains," December 1987. This document recommends a number of stabilization methods for riverside pits to prevent destabilization during a flood. One of the techniques is to install inlet and outlet structures in the pits to allow the floodwaters to flow nonerosively through the pit area. If the pits aze no[ subject to deep, high velocity floodwaters structural stabilization may not be needed. However, it appears that a lazge portion of the proposed operation falls within the `AE' flood zone as defined by the National Flood Insurance Program. This indicates that the pits may be subject to aggressive flooding. Many of the same stabilization techniques recommended by Urban Drainage and Flood Control are also